Interested in creating or using web 2.0-based activities or projects? Terry Freedman has compiled lots of information already.
http://www.ictineducation.org/free-stuff/

http://www.toondoo.com/ This is a site where students can create comic strips.

http://www.glogster.com/ This is a a site for interactive posters.

Want your students to create their OWN video games in class? This link to scratch is great and kids love it.
http://scratch.mit.edu/

Here is an article from the CNN Money website about Computer games in classrooms. it's very interesting and relevant.
http://money.cnn.com/2008/06/06/technology/games_change.fortune/index.htm

http://www.freetech4teachers.com/ this site has a lot of helpful resources.

www.polleverywhere.com This site will allow you poll students using cell phones to text in the answers, Great brainstorming tool.

http://deturl.com/ This site allows you to download YouTube videos onto your computer.
http://www.mediaconverter.org/ This site allows you to convert any video file format into another format for free in the browser, including YouTube videos. Limit of five conversions per day.

http://phet.colorado.edu/ This is an interactive simulations website that was produced out of University of Colorado, Boulder. It has simulations for all areas of science, math (mostly physics based, springs, vectors, etc.) and even "cutting edge research" activities that involve stretching DNA or making lasers fire. The website is easy to navigate and also includes descriptions of workshops for educators who want to pursue this sort of technology in the classroom.

http://www.socrative.com
Site for quick assessment creation. Good for pre/post assessments. Also good for surveys. Gives good data back.

Best Science Apps for kids (ages 4-21)

https://wise.berkeley.edu/
This site showcases lessons that can be taught through their website. The lessons and assessments are embedded on the website.